The present invention relates to a magnetic film for a magnetic device, which has a high saturation magnetization property, and a magnetic head for a hard disk drive unit and a solid device, each of which has the magnetic film of the present invention.
To improve recording density of a hard disk drive unit, intensity of a magnetic field, which is generated by a recording head, must be greater. In a conventional recording head, magnetic poles (cores) are made of a ferromagnetic material, and an electric current passes through coils winding around the magnetic poles so as to generate induction magnetic fields and converge the induction magnetic fields in the magnetic poles, so that a strong magnetic field for writing can be emitted in one direction.
If intensity of the induction fields, which are generated by the coils, are fixed, saturation magnetization of the magnetic poles are increased or the induction fields are efficiently converged so as to increase the intensity of the magnetic field for writing.
To increase the intensity of the magnetic field for writing, high saturation magnetization materials have been employed. They are a Ni—Fe alloy (permalloy), a Fe—Al—Si alloy (Sendust), a Fe—Co—Si—B amorphous alloy, a CO—Ni—Fe alloy, a Co—Fe alloy, etc.
When a recording head for a hard disk drive unit was firstly provided for a practical use, an Ni—Zn ferrite was used as a material for magnetic poles. At that time, only magnetic tapes were used as magnetic recording media. The Ni—Zn ferrite has high abrasion resistance and corrosion resistance, further has high resistivity so that eddy current loss can be prevented. However, the Ni—Zn ferrite has a disadvantage of small saturation magnetization, e.g., 0.4 T, as a material for magnetic poles.
At that time, magnetic poles were made by mechanical machining, but it was difficult to machine magnetic poles for small heads. To solve the problem, permalloy, etc., to which photolithography can be applied, are employed. Permalloy is a soft magnetic material invented in 19th century, it has relatively high corrosion resistance and its saturation magnetization is greater than that of ferrite, so that permalloy was used as a material for magnetic poles as well as ferrite. However, the saturation magnetization of permalloy is 1.0 T, so magnetic fields of permalloy poles are insufficient. Thus, high saturation magnetization materials are used these days.
Now a Fe70Co30 alloy is mainly employed as a material for magnetic poles. Its saturation magnetization is 2.45 T, which is the greatest as a simple substance. There are no substances having saturation magnetization greater than that of the Fe70CO30 alloy. Note that, data of a Fe16N2 film having saturation magnetization of 2.8-3.0 T was reported (see M. Komuro et al., Journal of Applied Physics, vol. 67, No. 9, pp. 5126(1990)). But, the data are now doubted, it seems to be 2.4 T or less (see M. Takahashi et al., Journal of Applied Physics, vol. 79, No. 8, pp. 5546(1996)). Namely, the saturation magnetization of Fe16N2 is smaller than 2.45 T of the Fe70CO30 alloy.
Experiment data of magnetic films similar to the magnetic film of the present invention were reported. In the experiment, saturation magnetization moment for one atom of Fe or FeCo was increased to 10 μm at the most in a dilute alloy in which Fe was dispersed in Pd, a Fe/Pd multilayered film and a FeCo/Pd multilayered film. Note that, saturation magnetization moment for one atom of Fe is 2.2 μm; that of Fe70CO30 is 2.46 μm. The phenomenon was caused by increasing saturation magnetization moment in a boundary surfaces between Fe atoms and Pd atoms. However, according to the data, if the film is entirely made of the Fe—Pd alloy (or the Fe—Co—Pd alloy), content ratio of Pd is much greater than that of Fe, so the saturation magnetization of the entire film must be very small. Therefore, the film cannot be practically used as a material of magnetic poles. In any films, high saturation magnetization were observed around vaporization temperature of liquid helium, i.e., around 2.4K; saturation magnetization moment was not increased at room temperature. The above described data are disclosed in Physical Review, vol. 125, No. 2, pp. 541 (1962); Journal of Applied Physics, vol. 77, No. 8, pp. 3965 (1995); IEEE Transaction on Magnetism, vol. 28, No. 5, pp. 2766 (1992); and Journal of Applied Physics, vol. 92, No. 5, pp. 2634 (2002).
To improve recording density of a hard disk drive unit, it is effective to use a high saturation magnetization material for a recording head. However, as described above, the material having the greatest saturation magnetization is the Fe70CO30 alloy, whose saturation magnetization is 2.45T. There are no materials having the saturation magnetization greater than 2.45T.